Biological Classification

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Simple use-based grouping was not enough to classify the huge variety of living organisms. As more microorganisms were discovered, especially bacteria, fungi, slime moulds, and unicellular forms, a cl…

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Aristotle used simple morphological characters. He classified plants into trees, shrubs, and herbs, and divided animals into those with red blood and those without red blood.

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Linnaeus proposed a two-kingdom system with Plantae and Animalia. Organisms were grouped mainly on the basis of form and constitution. This system was simple, but it could not place bacteria, fungi, a…

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Protista was added to overcome the difficulty of placing bacteria, slime moulds, and other unicellular organisms in only two kingdoms. Ernst Haeckel added Protista in 1866 to include bacteria, algae, …

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Robert H. Whittaker proposed the five-kingdom system in 1969 and created Fungi as a separate kingdom. The five kingdoms are Monera, Protista, Fungi, Plantae, and Animalia. The system is based on cell …

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The five criteria are: cell structure, body organisation, mode of nutrition, reproduction, and phylogenetic relationships. These helped separate prokaryotes, unicellular eukaryotes, multicellular plan…

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Monera includes primarily prokaryotic organisms. Protista includes eukaryotic, primarily unicellular forms. Plantae includes multicellular photosynthetic forms. Animalia includes multicellular animals…

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Lichens and some acellular organisms such as viruses, viroids, and prions are not mentioned in this system. They do not fit neatly into the five kingdoms.